Backpack



FIG. 1 is a perspective view of one embodiment of a backpack showing my new design;

FIG. 2 is a front elevation view thereof;

FIG. 3 is a rear elevation view thereof;

FIG. 4 is a right elevation view thereof;

FIG. 5 is a left elevation view thereof;

FIG. 6 is a top view thereof; and,

FIG. 7 is a bottom view thereof. 

I claim the ornamental design for a backpack, as shown. 